The invention relates to a valve unit, in particular for installations with pressure exchangers with tubular chambers through which flow occurs alternately, a rotatable control element with a plurality of flow paths being arranged within a housing, the housing having a plurality of connections for connection lines, the housing being connected to a first pipe system and, in each case, with an end of at least one tubular chamber, a respective other end of a tubular chamber being connected to a second pipe system with the intermediate connection of further valve units, the control element being provided with a motor-driven drive shaft and the flow paths of the control element being alternately connected to openings arranged in the housing.
Pressure exchangers of this type comprise two or more tubular chambers, whose ends are provided with valve units. The tubular chambers are alternately subjected to fluids of different energy content by appropriately opening and closing the valve units. Within the tubular chambers, it is therefore possible to transfer, in an installation or in a technical installation process, a high pressure of one fluid to another fluid which only has a low pressure. With the aid of such pressure exchangers, savings in energy costs can therefore be achieved within installations and pumps for increasing pressure can be made smaller.
A reverse osmosis process is often used for treating water. In this arrangement, a fluid flow to be cleaned is forced at high pressure through a membrane system which, in the case of large fuel quantities, consists of a large number of membrane modules. In such membrane modules, a separation into pure water and an enriched concentrate takes place through a membrane because, invariably, only a part of the fluid to be cleaned can flow through a membrane. The proportion which flows through the membrane emerges as pure water, also referred to as permeate, on the other side of the membrane as a usable proportion. The part which does not flow through the membrane leaves a membrane module as brine—a fluid concentrate enriched with salts and minerals—as an unusable proportion which is at high pressure. This pressure is approximately 2 bar below a module inlet pressure of approximately 65 bar.
U.S. Pat. No. 5,306,428 discloses a reverse osmosis installation in which pressure exchangers in the form of tubular chambers are used for recovering energy. With the aid of these tubular chambers, the pressure of the energy-rich brine flowing away from the membrane module, which is still high, is transmitted to a fluid which still has to be cleaned. A lower pump drive power, by the amount of this increase in pressure, is therefore necessary in order to generate the high pressure necessary for the reverse osmosis process in the fluid to be introduced.
In order to control and/or switch over the fluid paths, of the brine in and out of the tubular chambers of the pressure exchanger, a valve unit with a rotating control element is used, together with other valve units. With the aid of this control element, the tubular chambers of the pressure exchanger are alternately subjected to the brine emerging from the membrane modules. The rotating control element is configured as a cylinder in which connecting ducts are arranged in the manner of a 3-way valve. During the switch-over procedures, all the flow paths are completely blocked. In order to avoid pressure surges during such switch-over procedures, pressure balance ducts are arranged within the cylinder.
The separation capability of a membrane decreases as a function of the duration of operation of the membrane and a fluid to be cleaned must remain correspondingly longer within a membrane module. For this reason, the switch-over times of the cylinder are influenced, in the prior art, with the aid of a servomotor. This valve unit, however, is only suitable for small reverse osmosis installations because the flow cross sections within the valve unit are approximately the same size as the flow cross sections of the ducts to be filled. In the case of large installations, and the fluid columns to be displaced in them and the forces caused by this, a substantial dimensioning problem arises for the valve unit.